1. Technical Field
The present invention relates to an electronic circuit such as time constant circuit or resonance circuit including a capacitor. Further, the present invention relates to a pen-shaped position detector used together with a coordinate input device.
2. Description of the Related Art
In an electronic circuit such as time constant circuit or resonance circuit including a capacitor, the capacitance of the capacitor is adjusted in an early stage for adjustment as a product. This adjustment is intended to set a time constant so as to provide constants unique to electronic equipment or set a resonance condition so as to match the resonance frequency with a unique frequency. At this time, the capacitance of the capacitor is adjusted, for example, using a trimmer capacitor.
On the other hand, an electromagnetic induction coordinate input device includes a sensor and pen-shaped position indicator as disclosed, for example, in Japanese Patent Laid-Open No. 2002-244806. The sensor includes a number of loop coils disposed in the directions of the x and y coordinate axes. The position indicator has a resonance circuit that includes a coil and capacitor. The coordinate input device detects the coordinates in the x- and y-axis directions of the position indicated by the position indicator based on electromagnetic induction taking place between the position indicator and sensor. The x- and y-axis directions are respectively the horizontal and vertical directions of the substrate on which the many loop coils are disposed, for example, in the sensor.
The resonance frequency of the resonance circuit of the position indicator is selected to ensure that the resonance circuit resonates with the frequency signal from the sensor. In related art, a trimmer capacitor including an adjuster adapted to adjust the capacitance thereof is used at least as part of the capacitor making up the resonance circuit for selecting the resonance frequency. This adjuster is manipulated to adjust the electrostatic capacitance of the trimmer capacitor to a desired resonance frequency.
Alternatively, a plurality of chip capacitors are provided in advance rather than using a trimmer capacitor. Of the plurality of chip capacitors, the number of the chip capacitors to be enabled is selected in such a manner that those chip capacitors to be disabled are disconnected from the circuit, thus achieving a predetermined resonance frequency.